1. Field of the Invention
The present invention relates to the measurement and recording of vehicle traffic and, more specifically, to the count of vehicles moving on a street, measuring the velocity of the vehicles, and determining the relative direction of travel of the vehicles. The present invention is referred to herein as an Optronic System because it integrates an optical light beam emitting and sensor system, sensing light beam interruptions with current state-of-the-art electronics, and digital processing of the vehicle traffic measurements into useful engineering data form. The Optronic System does not sacrifice accuracy for portability, and the system can be moved from one location to another traffic measurement location and set-up quite easily in 15 minutes or less. The Optronic System eliminates the need for embedding inductance type sensors in the pavement of a street, especially at a busy intersection, or taping xe2x80x9chosesxe2x80x9d to a street surface.
2. Description of the Related Art
The measurement of vehicle traffic (the number of vehicles passing a location on a street, the direction in which the individual vehicles are traveling, and most importantly the velocity at which individual vehicles are moving on the street) is vital to the traffic engineers and law enforcement personnel of large communities as part of their traffic engineering and public safety responsibilities and activities. Accurate measurements of traffic are necessary at locations where vehicle and pedestrian traffic conditions are hazardous to vehicle operators and/or pedestrians, and the measured vehicle traffic data must be properly analyzed to identify effective solutions for resolving the safety problem or abating the unsafe conditions.
The present traffic measurement system used primarily by traffic engineering personnel is referred to herein as a pneumoelectronic system, since the system is a combination of pneumatic and electronic components and functions to measure the vehicle traffic. The pneumoelectronic system employs one or more pneumatic tubes (often referred to as xe2x80x9chosesxe2x80x9d) stretched across the street at the location where the measurement of the vehicular traffic is desired to be made. A functional description of the generic type of pneumoelectronic system presently in use is shown schematically in FIG. 1. The schematic in FIG. 1 (and all other Figures included in this document) is not to any dimensional scale, and the size/shape of the hardware units in the system cannot be determined from this functional schematic.
Also at present, vehicle traffic law enforcement personnel use radar equipment for measuring the velocity of moving vehicles, and using the results to control excessive vehicle speeding (as defined in the Motor Vehicle Code) which endangers other vehicles and pedestrians. Radar equipment improvements are constantly being made to improve the accuracy of the measured vehicle velocities, particularly in the moving mode of operation, but the other important aspects of vehicle traffic (counting the number of vehicles and determining their direction of travel at a specific location on a street for traffic engineering use) is not possible with present radar equipment.
The need for an improved traffic measurement system, which can be of more effective use, for example, to both traffic engineering and law enforcement personnel, becomes apparent after considering the limitations and shortcomings of the present traffic measurement systems (pneumoelectronic and radar).
Pneumoelectronic Counting of Vehicles
The measurement of vehicle traffic presently is done with a one- or two-pneumatic tube (each tube sealed at one end) system stretched generally parallel across a street surface in a near-orthogonal orientation to vehicle traffic, as indicated schematically in FIG. 1. The tube system (one or two non-metallic xe2x80x9chosesxe2x80x9d of substantial length) is fastened by an installation technician to the street surface, typically with multiple, wide, long strips of an adhesive tape. The unsealed end of the tube(s) are then attached to an electronic box (referred to herein as the data unit), which is typically located in a median strip or on the sidewalk adjacent to the street (or on the shoulder of the street when no sidewalk exists). The data unit is normally not physically located in the traveled portion of the street, as passing vehicles could roll over the data unit and incur crushing damage to the data unit and/or cutting damage to the tires of the vehicle.
The pneumatic tube system is connected through an attachment port on the data unit exterior so as to pass pressure pulses generated in the tube(s) into a pulse sensor (typically an electromechanical pressure transducer) in the data unit. When the front wheels of a vehicle pass over a tube, a pressure pulse is transmitted pneumatically to the pulse sensor which senses the increase in pressure of the pulse. When the pressure pulse is first sensed, the pulse sensor (which functions essentially as a pressure-activated electrical switch) outputs an electrical signal indicating the traffic event (i.e., that a vehicle wheel has passed over and compressed a tube) has taken place. When a count of the number of vehicles passing a selected location on a street is the only traffic parameter of interest to traffic engineering, it is necessary to install only a single detector capable of sensing the passing of the vehicles at that location. Each vehicle wheel passing over a tube compresses the tube and creates a pressure wave traversing through the tube. Two pulses in pressure will be introduced into the single tube by the wheels on the first two axles of a multi-axle vehicle passing over the tube and with a short time interval between the two pulses.
When activated by each pressure pulse, the pulse sensor in the data unit transmits an electronic signal to a multi-function processor, one function being to count the passing of each axle (since all wheels on one axle simultaneously passing over the single tube will result in only one pulse) of each vehicle. Two pulses in rapid sequence are interpreted by the processor as having been generated by the first and second axle of one passing multi-axle vehicle. The sensing logic in the signal processor typically has a xe2x80x9cprocessing pausexe2x80x9d after the initial two pulses so as not to count vehicles with more than two axles as being more than one vehicle. The processor then causes a simple counter device to add a unit count into a cumulative count of the number of vehicles passing over the tube(s) in the vehicle traffic volume measurement time period. The cumulative count is typically stored on a recording device also within the data unit, along with the essential date and time of each vehicle passing event to describe the numerical flow of traffic on a time-line basis. These traffic data recordings (referred to herein as line data) are electronically down-loaded from the data unit at the end of the measurement session and printed in hard copy for subsequent analysis by traffic engineering.
The velocity of the passing vehicles is also a traffic parameter of high interest to traffic engineers to study the rate of flow and individual speed of the vehicle traffic passing along a street. When it is desired to both count the number of vehicles passing a location on a street and to also record at what velocity the individual vehicles are traveling, more than one sensor is needed. In order to determine the velocity of vehicles using the pneumoelectronic system, two separated parallel tubes must be installed across the lane(s) of traffic to measure the time interval elapsed by a vehicle passing between the two tubes. As indicated in FIG. 1, the second tube is stretched across the street parallel to and at some pre-selected reference distance, DRef (typically 8 feet), from the first tube. The second tube is typically fastened to the street surface in the same manner as was done for a single tube (vehicle count only) installation. The second tube also is typically connected to the first tube with a tee connection (at some location where the tee connector will also not be crushed by a passing vehicle) a short distance before the single tube entry port on the same data unit (as previously described to count the number of passing vehicles). In this two-tube arrangement, the passing of each set of the vehicle wheels on an axle over either tube produces a characteristic single pressure pulse (generally of semisinusoidal waveform) transmitted into the pulse sensor within the data unit. After sensing the first two pulse signals in a passing-vehicle traffic event, the processor then xe2x80x9clocks outxe2x80x9d the remaining pulse signals from the vehicle pulse set (a two-axle vehicle passing over the two tubes will cause four pulses to be transmitted, and a 3-axle vehicle passing over the two tubes will cause six pulses to be transmittedxe2x80x94the number of vehicle axles multiplied by the number of tubes). After approximately one second from the time of xe2x80x9clock outxe2x80x9d, the system resets itself in preparation for the detection and processing of the next set of pressure pulses generated by the next vehicle passing over the two tubes.
As indicated earlier in this description of the pneumoelectronic system, the pulse sensor serves as an electrical switch and causes an electrical current to pass when the pressure input reaches a pressure level at which the switch has been designed to activate. When the first electrical signal is generated from a pressure pulse event (i.e., when the front wheels of a moving vehicle pass over the first tube) is received (from the pulse sensor) at the processor within the data unit, a timer device is started. When the second electrical signal is generated from the next pressure pulse event (i.e., when the wheels on the first axle of the moving vehicle also pass over the second tube) is received at the processor, the timer device is stopped. The time interval, xcex94t, between the first and second pressure pulses (xcex94t=tpulse 2-tpulse 1) is measured (to the nearest 0.01 seconds) using the timer device much like a stop-watch at a sport racing event.
The elapsed time it takes for the wheels on the front axle of a vehicle to sequentially pass over each of two tubes (fastened near-orthogonal to the vehicle path vector and parallel to each other) is a function of the vehicle velocity and the distance between the two tubes. Table 1 indicates the length of time (measured in seconds) taken by a vehicle moving at various constant velocities to travel through a reference distance, DRef. Typically in pneumoelectronic system installations, DRef is selected at 8 feet between the two tubes, because the distance (xe2x80x9cwheelbasexe2x80x9d) between the front and rear axles of small automobiles is generally more than 8 feet (i.e. wheelbases of almost all vehicles are more than 96 inches). This distance of 8 feet assures that the first axle of virtually all motor vehicles will pass over both tubes before the second axle encounters a tube. (Bicycles occasionally passing over the two tubes cannot be discerned by the pneumoelectronic system as not being motor vehicles, and they will be included in the vehicle traffic count made with the tube-type system.)
The equation for calculating the velocity of an object traveling at near constant speed for a known short time duration through a known short distance is found in the Laws of Motion (stated in any standard Laws of Physics reference book as: Velocity (V)=Distance (S)÷Time (t)). Table 1 was constructed using the equation (t=S÷V) to find the time lapsed when the object has a known velocity and passes through a known distance.
If the time increment is measured for the time it takes for a vehicle to travel between two tubes a known distance apart, the average velocity of the vehicle can then be calculated using the equation from the Laws of Motion:
V(mph)=kxc3x97DRef(ft)÷xcex94t(secs), (where k=0.6818 mph per fps).
As can be seen in the equation, the accuracy of the calculated velocity (V) is dependent on the accuracy of the measured lapsed time xcex94t, as well as on the accuracy of the reference distance DRef. (The conversion factor k is mathematically derived to be accurate to the significant places of the number shown). A timer having an accuracy of xcex94t=xc2x10.01 seconds is seen to produce a measured and recorded time between two pulses with marginal accuracy at the lower speeds (below 35 mph) primarily of interest to traffic engineers in studying traffic flow. At speeds above about 35 mph, the region of primary interest to law enforcement personnel, a timer having xcex94t=xc2x10.01 seconds accuracy is not adequate for measuring the time interval xcex94t for a vehicle moving between two tubes spaced 8 feet apart. For the latter reason, law enforcement personnel almost exclusively rely on radar type equipment to directly measure the speed of the higher speed vehicles with much better (but certainly not extreme) accuracy compared to the velocity indirectly determined with a pneumoelectronic system.
Frequently, one of the shortcomings of the tube-type installation is the adhesive tape being peeled back from the road surface by the traction of a vehicle""s wheels passing over the tape, allowing the tube to move significant distances (sometimes as much as 5xe2x80x3) laterally. If the objective of the traffic measurement is to obtain only a vehicle count, a loose tube does not affect the accuracy of the vehicle count. This same problem of the adhesive tape losing adhesion and allowing the tube to move laterally is encountered with a two-tube installation. If the objective of the traffic measurement is to obtain the vehicle count and the direction of travel of each measured vehicle, two loose tubes also do not affect either the count of the vehicles or the determination of their direction of travel. However, if the measurement objective is to obtain reasonably accurate vehicle velocity measurements, as well as obtaining the count and direction of travel of the vehicles, a loose tube (one or both in a two-tube installation) is unacceptable for accurate velocity determination.
There are several xe2x80x9cifsxe2x80x9d which individually or in combination can severely affect the accuracy of traffic measurements with the pneumoelectronic system. If the vehicle velocity is constant as the vehicle passes over the two tubes, if the two tubes are reasonably parallel across the street and reasonably orthogonal to the passing traffic, if the two tubes fastened to the street surface maintain the pre-selected reference distance DRef within reasonable accuracy, if the passing vehicle is the only vehicle introducing the first two pulses into the two tubes (a second vehicle passing over the two tubes in the opposite direction at the same approximate time as the first vehicle could contaminate the pulse data sensed), and if the timer measurement of the time interval between the first two sensed pulses was more accurate (i.e., measuring xcex94t to xc2x10.001 seconds), the two-tubes pneumoelectronic traffic measurement system would provide velocity measurements of sufficient accuracy for traffic engineering purposes. In a field environment, many of these xe2x80x9cifsxe2x80x9d are not always achieved, and normally this causes concern over the accuracy of the data. In any case, for law enforcement purposes, an accuracy of xc2x10.01 seconds for the timer measuring the time between pulses is not acceptable (i.e., a speeding violation could be challenged in a traffic court with near 100% success).
Table 2 indicates the range in calculated velocities for a timer which can measure a time increment xcex94t between pressure pulses to an accuracy of xc2x10.01 seconds (and with DRef=8 feet):
If the tubes are installed and maintain a DRef accuracy of 8 feet (96 inches) xc2x10.1 inch, there will be no significant reduction in the accuracy of the calculated velocity. However, if the two tubes are not installed at the same DRef distance as used in the velocity calculation, and/or are not installed with parallelism, and/or one of the tube attachments to the road surface loses adhesion (allowing the loose tube to move apart laterally with respect to the other tube), a change in DRef distance of 4-5 inches could result in a velocity inaccuracy of xc2x13 to xc2x14 mph. As another source of velocity inaccuracy, if both tubes become very loose in a two-tube installation and separate even further than 5 inches, this will generally cause the vehicle velocity to be calculated in an even more inaccurate manner (xc2x15 to xc2x17 mph). If the two tubes are installed at a DRef much closer than 8 feet separation distance, the same lateral change (due to looseness) in distance between the two tubes is a greater percentage of the smaller separation distance (reference distance DRef). The inaccuracy of the calculated vehicle velocity if DRef is 4 feet will be even greater (xc2x110 to xc2x114 mph). It is also for this accuracy reason that tubes are installed with the largest distance between them (8 feet), but not larger than the wheelbase of the smallest vehicles (which as stated earlier is generally at least 96 inches).
Depending on the combination of the several sources of inaccuracy, vehicle velocity data, especially that at the portion of the traffic velocity spectrum near or above the posted speed limit on the street being measured, potentially has a measured velocity inaccuracy of xc2x18 to xc2x110 mph using the two-tube technique. This is clearly not adequate for law enforcement purposes, and also must be considered by traffic engineers in their analysis of the measured vehicle velocity data.
The placement of two tubes physically across a street is recognized to have several other undesirable features, some of which are: (1) affixing the tubes on the street surface is a hazardous operation for the installing technician when the vehicle traffic is not safely detoured around the installation; (2) the tubes are at times dislodged from their attachment to the street surface and lose their reference distance and parallelism calibration; (3) the tubes are damaged too often by passing vehicles (especially by some speeding motorists who maliciously apply heavy braking or skidding as the wheels of their vehicles pass over the tubes); (4) the visual detection of two tubes across the street often causes vehicle operators detecting the tubes from a distance to slow down before passing over the tubes (which xe2x80x9cinfluencesxe2x80x9d the velocity data measurement); and (5) there are several possible error sources in the pneumoelectronic hardware components and pressure sensing interpretation producing data of questionable accuracy.
Another source of inaccuracy in the measured and calculated velocity of a vehicle occurs when the two tubes are installed across the street such that the DRef through which the vehicle passes is not the same as the DRef used in the calculation of the vehicle velocity. Human error is always possible, and the installing technician may set the two tubes at an erroneous DRef distance apart, or at some angle other than 90xc2x0 to the travel path of the vehicle. However, this adverse event occurs most often in the installation of a pneumoelectronic type system when the adhesive strips attaching the tubes to the street surface lose their adhesion and allows the tubes to laterally move (increasing or decreasing the DRef) as the wheels of a vehicle pass over the tubes.
The shortcomings of the present pneumoelectronic equipment to accurately and safely measure vehicle direction and velocity, as described heretofore, dictates the need for an improved (i.e., more accurate) means of simultaneously measuring the three primary vehicle traffic parameters, especially vehicle velocity. Because law enforcement personnel require a much more accurate measurement of vehicle velocity than is available with a pneumoelectronic system, radar type equipment is employed by law enforcement personnel to measure the velocity of individual vehicles.
Radar Measurement of Vehicle Velocity
For completeness in describing the techniques presently in use for measuring traffic parameters, the attributes of measuring vehicle velocity with radar equipment is included herein. The acronym RADAR (which has become the noun xe2x80x9cradarxe2x80x9d in common usage) is derived from its original title RAdio Detection And Ranging. Radar was developed by allied military countries during the early 1940s into a practical means for detecting the presence of an object in the beam path of the radar system, for indicated angle from the zero azimuth angle axis of the radar emitter to the detected object, and for estimating the distance from the radar emitter to the object. Ground-based stationary radar systems were also used to estimate the altitude of aircraft through simple trigonometric calculations performed with the radar estimations of slant distance and angle of inclination from the radar to the aircraft. Radar was not initially developed to be an accurate velocity measuring technique because it used broad-bandwidth radio wavelength radiation which does also sense the motion of secondary objects in the periphery of the primary moving target. Narrow-bandwidth radar equipment with laser pointers to target and measure the velocity of a specific vehicle among a group of moving vehicles is only recently coming into availability to law enforcement personnel for more accurate vehicle velocity measurements.
Radar equipment does have the unique advantage of being able to be operated while in motion (such as in the vehicle of a law enforcement officer) and achieve an acceptable level of accuracy of velocity measurement while accounting for the relative motion between the vehicle-based radar and the target vehicle. Additional corrections are mathematically applied to the moving radar detections to account for the difference in relative velocities between the radar and the target, which must be done to convert the radar information into an absolute velocity of the target vehicle (i.e., miles per hour (mph) relative to the stationary road surface). This introduces further sources of inaccuracies into the measurement and measurement processing. If the indicated velocity (displayed on the operator""s dashboard speedometer and input into the radar processor) of the law enforcement vehicle is not accurately calibrated for use in the calculation, an error will be introduced into the relative velocity between the two moving vehicles. This error will manifest itself in the radar equipment displaying an inaccurate velocity for the target vehicle. Currently, only the radar system has this capability of measuring the relative velocity of another moving vehicle while itself is in motion. Existing and emerging fixed-base traffic measurement systems (pneumoelectronic, and embedded inductance loops) cannot practically incorporate any technology that would permit their use in a motion mode.
One disadvantage of the use of radar speed measurement equipment is that it requires a human operator (with attendant personnel costs, but more importantly with the attendant possibility of human error) to operate the radar system in field locations, and to interpret real-time what the indicated velocity displayed means. Law enforcement personnel cannot be present everywhere to assess with radar equipment whether the speed of an individual vehicle is dangerously above the safe speed for the conditions existing at that location on a street (e.g., in a school zone, at a crosswalk, or near a park) or relative to other moving vehicles on that street.
Returning to the description of the present pneumoelectronic traffic measurement system, to determine the direction of travel (i.e., from left to right or from right to left relative to the data unit) of a moving vehicle requires being able to distinguish which of the two pulses in a two-pulse set was created in which tube first. Vehicle direction cannot be determined with a single tube (or any single detector) installation. The two-tubes pneumoelectronic system most frequently merges the input pulses from the individual tubes prior to the pulses entering the data unit, and the pulse sensor interprets these as being two sequential pulses from a single vehicle passing over one tube. The processor function within the data unit is capable of calculating the velocity of the passing vehicle but is unable to discern which pulse was produced in the left or right tube, and therefore is unable to determine the direction of travel of that vehicle.
To obtain more accurate measurements of a vehicle velocity for both traffic engineering and law enforcement purposes than is possible with most present pneumoelectronic traffic measurement systems, to obtain a measurement of the vehicle direction on the street (not always possible with the present pneumoelectronic system), and to avoid the several xe2x80x9creal-worldxe2x80x9d problems being experienced with the present pneumoelectronic system (i.e., tubes having to be fastened on a street surface with vehicles moving by in close proximity to the installing technician and being damaged by traversing vehicles, or their reference separation distance being changed by vehicles passing over them requiring maintenance of the tube installation), an improved and accurate measurement system is needed.
It is, therefore, an object of the present invention, to wit an Optronic System, to provide a vehicle traffic measurement system in which more than one of the disadvantages of the prior art are overcome. In accordance with this objective, there is provided according to the invention a vehicle traffic measuring system comprising a beam emitter unit comprising a first power source and at least two laser beam emitters operatively interconnected to said first power source; a detachable control display subunit comprising a second power source, a beam status discriminator operatively interconnected to said second power source, a pulse oscillator operatively interconnected to said second power source, an electronic chip comprising an electronic timer and clock operatively interconnected to said second power source, a processor operatively interconnected to said second power source, a data recorder operatively interconnected to said second power source, and a display panel operatively interconnected to said second power source; and a sensor control unit comprising at least two laser beam sensors operatively interconnected to said second power source.
There is also provided according to the invention a method of counting individual moving vehicles comprising the steps of generating at least one laser beam from a first unit to a second unit, interrupting said laser beam(s) with a moving vehicle, sensing said interruption(s) of said laser beam(s), processing said sensed interruptions into electronic count data, recording said electronic count data, and formatting and generating a list of said electronic count data into a usable format.
There is also provided according to the invention a method of determining individual vehicle velocity and direction of travel comprising the steps of generating at least two laser beams from a first unit to a second unit, interrupting said laser beams with a moving vehicle, sensing said interruptions of said laser beams, processing said sensed interruptions into electronic velocity and direction of travel data, recording said electronic velocity and direction of travel data, and formatting and generating a list of said electronic velocity and direction of travel data into a usable format.
There is further provided according to the invention a method of counting, determining the velocity and direction of travel of individual vehicles comprising the steps of generating at least two laser beams from a first unit to a second unit, interrupting said laser beams with a moving vehicle, sensing said interruptions of said laser beams, processing said sensed interruptions into electronic count, velocity and direction of travel data, and formatting and generating a list of said electronic count, velocity and direction of travel data into a usable format.